Combustion control system



all

Oct. 27, 1964 P. GIUFFRIDA 3,154,724 COMBUSTION CONTROL SYSTEM Filed 001;. 9, 1961 United States Patent 3,154,724- QOWUSTEUN QQNTRQL SYSTEM Philip Giufirida, North Andover, Mass, assignor to Electronics orporation of America, tjambridge, Mass, a corporation of Massachusetts Fiied Get. 9, 1961, Ser. No. 143,9fl? 16 Claims. (Ci. 3l7 -l3il) This invention relates to combustion control systems and more particularly to a combustion control system involving the sensing of radiation emanating from flame in the combustion chamber.

In the supervision of combustion systems it is desirable that a characteristic unique to the flame itself, in contrast with the interior of the combustion chamber or other extraneous environmental factors, be sensed so that the presence of either the main combustion flame or the pilot flame at the burner may be reliably detected. A variety of systems have been proposed for supervising combustion and systems which employ an infra red radiation sensitive device have been particularly successful. Such a radiation sensitive device is sensitive to particular wavelengths of radiation from the flame under investigation. However, the supervised combustion systems frequently include other sources of similar radiation and it is essential to distinguish between the radiation emanating from the flame and that from the extraneous sources. It has been discovered that the infrared radiations from the combustion flame have a fluctuating characteristic and lead sulphide sensing cells utilized in conjunction with a band pass amplifier arrangement tuned to pass a narrow band of frequencies corresponding to the most pr dominant flame fluctuation frequency of the type shown in the Cade patent, No. 2,811,711 provide excellent flame supervision systems. In some combustion systems, however, such as those employing multiple burner combustion chambers, for example, in which it becomes necessary to monitor each flame independently for safety reasons, infra red systems of detection are not completely suitable, as the infra red radiation emanates from the entire flame beyond in a flame fringe area so that discrimination between the several flames within the same combustion chamber is diflicult, if not impossible. The individual flames may be more easily supervised by sensing a radiation source that is more localized, such as a source of ultraviolet radiation frequencies, which emanate only from the core of the flame. In addition, ultraviolet radiation sensing is more reliable than other systems of flame detection as it is less subject to interference from radiation sources other than the flame itself. However, complex control circuitries have been developed and proved to be reliable operating in conjunction with the infra red sensing systems, and accordingly it is an object of the invention to provide a novel and improved combustion control system that employs an ultraviolet detector in a manner to be compatible with existing combustion control circuitry that utilizes reliable, low fre quency narrow band pass amplifier control arrangements.

Another and more general object of the invention is to provide a novel and reliable combustion control sy tem which utilizes a flame sensing element sensitive to radiation of the ultraviolet range.

In accordance with principles of the invention there is provided a combustion control system which employs a quantum detector sensitive to ultraviolet radiation in the flame being supervised. The quantum detector may be disposed in a scanner arrangement so that it supervises both the pilot flame and the main flame in the combus tion system or it may supervise one flame while an infra red detector supervises another flame. The preferred embodiment of the invention employs a. quantum detector 3,l54,?24 Patented @et. 27, l'gfid having two spaced electrodes between which an electrostatic field is periodically built up to a magnitude sufiicient to produce avalanche breakdown between the electrodes when an electron is freed from one electrode in response to ultraviolet radiation impingement on that electrode. The electrostatic field build-up cycle is limited to a low frequency rate in the order of less than twenty-five cycles per second and in the preferred embodiment is created by a resistance capacitance network arrangement in which the values of the components are proportioned to achieve this desired maximum cycle frequency. The output of the detector circuitry is coupled by a damped tuned circuit of predetermined frequency characteristics to a multi-stage band pass amplifier circuit that operates the main combustion control relay. The amplifier-control relay circuitry is also compatible with infra red detector systems. The system thus provides a versatile combustion supervision system which employs ultraviolet radiation detection circuitry as Well as infra red detection, and in which either type of detection may be used individually or together.

Other objects, features and advantages of the invention will be seen as the following description of a preferred embodiment thereof progresses in conjunction with the drawing, in which:

FIG. 1 is a schematic diagram of the scanner arrangement showing the main burner, the pilot burner and the scanner element disposed for supervising both the pilot flame and the main burner flame; and

FIG. 2 is a schematic diagram of the ultraviolet radiation detection and band pass amplifier circuitry according to the preferred embodiment of the invention.

in FIG. 1 there is shown in diagrammatic form a combustion system having a combustion chamber 10 which is supplied with a main fuel conduit 12 controlled by suitable valving (not shown). A pilot burner 14, provided with suitable means for ignition provides a pilot flame 16 which extends out into the area in front of the main fuel conduit 12. The fuel from the conduit 12 is ignited by the pilot flame to provide a main flame 18. Mounted in the wall of the combustion chamber is a tubular arrangement 20 which may be aligned so that both the end of the pilot flame 16 and the main flame 18 may be supervised by the scanner element 22.

The scanner element in this embodiment is an ultraviolet sensing tube which includes a pair of parallel, spaced tungsten electrodes 2-4, 26 as indicated in FIG. 2, which are housed in an envelope 23 transparent to ultraviolet radiation that contains a suitable inert gas. This scanner tube may be the commercially available McGraw-Edison ultraviolet radiation detection tube. The scanner element 22 is connected in series circuit with a current limiting resistor fit} of 10K ohms to a circuit arrangement which periodically builds up an electrostatic field of suflicient magnitude between the electrodes 24, 26 to permit avalanche breakdown between the electrodes in response to bombardment of those electrodes by ultra violet radiation protons. The electrostatic field control circuitry includes an 0.982 microfarad capacitor 3.2, a 470K ohm resistor 34, rectifying diode 36 and a high voltage transformer 38, which has a primary winding 4% to which a volt AC. input signal is applied and a secondary winding 42 connected between diode 36 and ground. The electrical time constant of the circuitry is such that the circuit restores the charge on capacitor 31, to the operative level after each tube breakdown at a maximum rate of less than twentydive cycles per second. In the preferred embodiment the circuit time constant is .038 second and it requires approximately 1% time constants (.048 second corresponding to a maximum rate of twenty-one cycles) to reach the operative charge sassy 2a a primary winding of output transformer 46. When the capacitor charge level is reduced to the drop across tube 22 the tube extinguishes (ceases conduction) and the charge level on capacitor 32 commences to be restored. Connected across the primary winding of the transformer 46 is a series combination of a 100% ohm resistor and an 0.068 infra red capacitor 563 which form a damped resonant circuit. Capacitor d stores up the steep Wave front and pulse that resulted from the avalanche discharge of tube 22 and the resonant characteristic of this output circuit converts this energery into a low frequency (less than twenty-five cycles) sine wave signal that is inductively coupled by the secondary 52 of transformer 46 to terminals 54 and 5d of the control relay operating circuitry.

That circuitry includes a main transformer 53 which supplies a B+ signal to the anodes of amplifier tubes as and 62 through the filter network that includes registers 64-6, diode 6d and capacitors 76-72. A biasing signal is also applied at terminal 54 through resistor 74. The input signal from the ultraviolet radiation detecting element 22 is coupled by capacitor '73 (which performs a DC. isolation function) and the resistor network including resistors lid and 81 to the grid of the fir" amplifier stage 64). A portion of the resultant output signal from the anode of stage till is fed back through the filtering network including capacitors 32 and 8 and resistors $6, 83 to the grids of tube dd as a low pass frequency control function (corresponding to the frequency of the damped resonant circuit and thus less than twenty-five cycles) and a second portion is coupled to the second amplifier stage via capacitor 9% and resistors 92 and 93. That stage is similarly arranged with a low pass (less than twenty-five cycles) capacitor feedback circuit which includes capacitors M, 96 and resistors 9i 1%. The resultant amplified output pulse is coupled by capacitor W2 through a rectifying circuit that includes diode 164 so that only negative pulses are applied to the RC integrating circuit including resistor res and capacitor 1%.

The output of the integrating circuitry is applied to the main relay control circuitry in which tube 110 is normally conducting so that the resultant voltage drop across resistor 112 is sufficient to maintain the tube 114 in non-conducting condition. When sutficient negative charge has built up on capacitor Mid in response to input pulses produced in response to sensed ultraviolet radiation from the supervised flames, tube llltl is driven out of conduction and the change in voltage at its anode is coupled to the grid of tube 114, so that tube 114 conducts and energizes the control relay 12%). This relay when energized indicated the presence of flame.

it will be noted that the secondary of transformer 55 has a plurality of taps, and in addition to supplying the 13+ potential it also supplies a voltage to the tube filaments 122, a voltage to the relay 12th, and a voltage to the relay control tube circuit. A lead sulphide infra red radiation detector cell 124 may be used in certain combustion supervision applications where the ability to sense both infra red and ultraviolet radiation may be desirable. For example, a combustion system might supply pulverized coal as the main fuel with a gas fired pilot. As pulverized coal produced a flame of low ultraviolet content while gas flames produce substantial quantities of ultraviolet radiation, the detector 22 may be disposed to supervise the pilot flame 16 only and the cell 124 may be disposed in a separate arrangement to supervise the main flame 18. For example, the cell 12 may be connected in series with the secondary 52 of transformer 46 while a switch 125 in parallel with cell 324 permits the infra red detector to be removed from the circuitry. The switch might be operated in response to conventional programmer control, for example.

The invention provides a reliable band pass amplifier, combustion control relay arrangement operative at a low flame flicks frequency (the band pass filters have maximum signal pass characteristics at about 10 cycles per second, thus excluding steady state signals as well as power frequency signals and other signals which might cause erroneous operation), in combination with an ultraviolet radiation detector circuit, compatible with the band pass amplifier, which supervises the flame within a combustion system.

While a preferred embodiment of the invention has been shown and described it will be obvious to those having ordinary skill in the art that certain modifications may be made therein without departing from the invention. Therefore it is not intended that the invention be limited thereto or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

I claim: 7 a 1. A combustion control system comprising a quantum W detector sensitive to ultraviolet radiation from a flame,

said quantum detector being arranged to supervise flame in a combustion chamber, and including a pair of electrodes housed in an envelope transparent to ultraviolet radiation, means to energize said quantum detector so that said detector generates pulse signals at a predetermined frequency of less than twenty-five cycles persecond when flame is sensed by said detector, coupling means to couple a signal resulting from a breakdown between the electrodes in said quantum detector upon sensing of ultraviolet radiation from said flame, band pass amplifier means connected to said coupling means, the band pass characteristics of said amplifier including said predetermined frequency, and operating control means responsive to said amplifier for indicating the flame condition in said combustion chamber.

2. The combustion control system as claimed in claim 1 wherein said detector energizing means includes a resistance capacitance circuit arranged to apply an electrostatic field to said detector electrodes at a frequency of.

less than twenty-five cycles per second when said electrodes are exposed to ultraviolet radiation.

3. The combustion control system as claimed in claim 1 wherein said coupling means includes a damped resonant circuit tuned to provide an output signal having a principal frequency of less than twenty-five cycles per second in response to each breakdown of said quantum detector.

4. The combustion control system as claimed in claim 3 wherein said damped resonant circuit include a primary winding of a transformer connected in series with said quantum detector and the series combination of a capacitor and a resistor connected in parallel with said primary winding. 7

5. A combustion control system for supervising a pilot flame and a main flame in a combustion chamber comprising a flame condition indication relay, a band pass amplifier being connected to said flame condition indicating relay to provide a signal to operate it, said amplifier being arranged to produce said relay operating signal in response to input signals within the frequency range of five to twenty-five cycles per second only, detector means having a pair of spaced electrodes disposed in an ionizable gas, said detector'adapted to be disposed to supervise an area within said combustion chamber, means to energize said detector means so that said detector means periodically generates pulse signals in response to avalanche breakdown of said ionizable gas when flame is sensed by said detector means, means to convert said avalanche breakdown pulses to an output signal having a major frequency component within said band pass frequency range, and means to apply said output signal to said band pass amplifier to operate said flame responsive relay.

6. The combustion control system as claimed in claim wherein said pair of electrodes are housed in an envelope transparent to ultraviolet radiation, and said energizing means produces a high voltage electrostatic field between said electrodes at a frequency of less than twentyfive cycles per second and includes a high voltage source, a capacitor connected across said high voltage source, and a resistance connected in circuit between said capacitor and said high voltage source, the values of said resistor and said capacitor being proportioned so that the repetitive build-up of an electrostatic field of sulficient magnitude to enable an avalanche breakdown to be pro duced between said electrodes in response to ultraviolet radiation can occur at a maximum rate of twenty-five times per second.

7. The combustion control system as claimed in claim 5 wherein said avalanche breakdown pulse converting means includes a transformer having a primary winding and a secondary winding, a resistance and a capacitance connected across said primary winding, providing in combination a damped resonant circuit for converting said avalanche breakdown pulse to said output signal, said primary winding being connected to said detector means and said secondary winding being connected to said band pass amplifier for coupling said output signal to said amplifier.

8. A combustion control system for supervising a pilot flame and a main flame in a combustion chamber comprising a flame condition indicating relay, a band pass amplifier being connected to said flame condition indicating relay to provide a signal to operate it, said amplifier being arranged to produce said relay operating signal in response to input signals within the frequency range of five to twenty-five cycles per second only, first detector means disposed to supervise a first selected portion within said combustion chamber, said first detector means being responsive to infra red radiation and producing a first output signal having a major frequency component corresponding to the major frequency component of the sensed infra red radiation, a second detector means disposed to supervise a second area within said combustion chamber, said second detector means providing an avalanche breakdown pulse when subjected to ultraviolet radiation, means to convert said avalanche breakdown pulse to a second output signal having a major frequency component within said band pass frequency range, and means to apply said first and second output signals to said band pass amplifier to operate said flame responsive relay.

9. The combustion control system as claimed in claim 8 wherein said second detector means is a quantum detector that includes a pair of electrodes housed in an envelope transparent to ultraviolet radiation, means to produce a high voltage electrostatic field between said electrodes at a frequency of less than twenty-five cycles per second including a high voltage source, a capacitor connected across said high voltage source, and a resistance connected in circuit between said capacitor and said high voltage source, the values of said resistor and said capacitor being proportioned so that the repetitive build-up of an electrostatic field of suflicient magnitude to enable an avalanche breakdown to be produced between said electrodes in response to ultraviolet radiation can occur at a maximum rate of twenty-five times per second.

10. The combustion control system as claimed in claim 9 wherein said avalanche breakdown pulse converting means includes a transformer having a primary winding and a secondary winding, a resistance and a capacitance connected across said primary winding, providing combination a damped resonant circuit for converting said avalanche breakdown pulse to said second output signal, said primary winding being connected to said second detector means and said secondary winding being connected to said band pass amplifier for coupling said second output signal to said amplifier.

11. A combustion control system comprising flame condition indicating means,

band pass amplifier means connected to said flame condition indicating means to provide an indicating means operating signal,

said amplifier means having a band pass characteristic so that it produces said operating signals in response to A.C. input signals in the audio and subaudio frequency range only and rejects power frequency signals,

input circuitry including detector means sensitive to flame, means to energize said detector means so that said detector means periodically generates pulse signals at a frequency substantially different than said power frequency and wtihin the band pass region of said amplifier when flame is sensed by said detector means,

and coupling means to apply output signals from said detector resulting from the sensing of flame as input signals to said band pass amplifier.

12. The system as claimed in claim 11 wherein said detector means includes a pair of spaced electrodes housed in an envelope transparent to ultraviolet radiation and said energizing means creates an electrostatic field between said electrodes, the breakdown of which produces said output signal.

13. The combustion control system as claimed in claim 12 wherein sai-d electrostatic field creating means repetitively generates an electrostatic field between said detector electrodes at a frequency of less than twentyfive cycles per second when flame is sensed by said detector means.

14. The combustion control system as claimed in claim 12 and further including a first transformer having a. step up turns ratio for coupling said alternating signal to said energizing signal applying means and said coupling means includes a second transformer having a primary winding and a secondary winding, said primary winding being connected to said detector means and said secondary winding being connected to said amplifier means.

15. The combustion control system as claimed in claim 11 wherein said coupling means includes a damped resonant circuit tuned to provide an output signal having a principal frequency of less than twenty-five cycles per second in response to each signal resulting from a breakdown of the electrostatic field between said electrodes.

16. The combustion control system as claimed in claim 15 wherein said damped resonant circuit includes a primary winding of a transformer connected in series with said detector means and the series combination of a capacitor and a resistor connected in parallel with said primary winding.

References Cited by the Examiner UNITED STATES PATENTS 2,392,895 1/46 Adair 317128 X 2,721,276 10/55 Exner.

2,807,008 9/57 Rowell 340228 X 2,811,711 10/57 Cade et al. 340-428 2,879,456 3/59 Pinckaers 317-430 X 2,911,540 11/59 Powers 340-228 X SAMUEL BERNSTEIN, Primary Examiner. 

1. A COMBUSTION CONTROL SYSTEM COMPRISING A QUANTUM DETECTOR SENSITIVE TO ULTRAVIOLET RADIATION FROM A FLAME, SAID QUANTUM DETECTOR BEING ARRANGED TO SUPERVISE FLAME IN A COMBUSTION CHAMBER AND INCLUDING A PAIR OF ELECTRODES HOUSED IN AN ENVELOPE TRANSPARENT TO ULTRAVIOLET RADIATION, MEANS TO ENERGIZE SAID QUANTUM DETECTOR SO THAT SAID DETECTOR GENERATES PULSE SIGNALS AT A PREDETERMINED FREQUENCY OF LESS THAN TWENTY-FIVE CYCLES PER SECOND WHEN FLAME IS SENSED BY SAID DETECTOR, COUPLING MEANS TO COUPLE A SIGNAL RESULTING FROM A BREAKDOWN BETWEEN THE ELECTRODES IN SAID QUANTUM DETECTOR UPON SENSING OF ULTRAVIOLET RADIATION FROM SAID FLAME, BAND PASS AMPLIFIER MEANS CONNECTED TO SAID COUPLING MEANS, THE BAND PASS CHARACTERISTICS OF SAID AMPLIFIER INCLUDING SAID PREDETERMINED FREQUENCY, AND OPERATING CONTROL MEANS RESPONSIVE TO SAID AMPLIFIER FOR INDICATING THE FLAME CONDITION IN SAID COMBUSTION CHAMBER. 